Hi Agarwick,
Glad you're considering DotNetNuke for your needs. It sounds like it might be a reasonable fit for you.
DNN has its own skinning engine, which is roughly analogous to ASP.NET's master page system (many would argue that it's much more powerful and flexible). Skins are written either in html (with a metadata xml extension file) or more directly as an ascx file.
The calculator application you describe would likely require a custom module. Since you seem to describe it as javascript-heavy, it might not require much server-side code. Others will be able to point you to a number of templates and tutorials on this topic.
With respect to the forms you described, the feedback module might meet your needs, and if not there are quite a number of "form modules" out there that allow a user to build forms through the UI without the need for code. Many are inexpensive or free. This may meet your requirements.
Most of what you describe can be implemented by a non-developer. For those few things that do require greater sophistication, expect to have to write some code (with custom modules in particular), and expect to encounter a somewhat challenging learning curve as you get started with the framework (depending on your level of expertise with ASP.NET, and software development in general). There is no totally free lunch, so there will be some learning to do with DNN (or any CMS) on the front end to perform custom development.
Hope this helps!
Brandon